pfsense squid reverse proxy emails with attachments not sent via mac os

[kashtan]

Good afternoon, help please.
Is ms exchange, squid reverse proxy is configured.
Everything is OK, but if you connect mac os from an external network through Outlook or a native client, the letters go, but if you put an attachment in the sent letter, the letters hang in the outgoing ones and the client writes: the server is not responding.
Letters without attachments go fine on a poppy.
At the same time on Windows, on iPhones everything is ok.

They turn off reverse proxy and letters with attachments on a poppy go fine.

Can anyone come across?